# The Compressed Word Problem for Groups by Markus Lohrey

By Markus Lohrey

The Compressed be aware challenge for teams offers an in depth exposition of identified effects at the compressed note challenge, emphasizing effective algorithms for the compressed observe challenge in quite a few teams. the writer provides the mandatory heritage besides the newest effects at the compressed be aware challenge to create a cohesive self-contained ebook obtainable to desktop scientists in addition to mathematicians. Readers will fast achieve the frontier of present examine which makes the publication specifically beautiful for college students trying to find a presently lively learn subject on the intersection of staff conception and laptop technological know-how. The be aware challenge brought in 1910 via Max Dehn is without doubt one of the most vital choice difficulties in staff idea. for lots of teams, hugely effective algorithms for the be aware challenge exist. in recent times, a brand new approach according to info compression for delivering extra effective algorithms for be aware difficulties, has been constructed, by way of representing lengthy phrases over crew turbines in a compressed shape utilizing a straight-line application. Algorithmic thoughts used for manipulating compressed phrases has proven that the compressed observe challenge may be solved in polynomial time for a wide category of teams corresponding to loose teams, graph teams and nilpotent teams. those effects have very important implications for algorithmic questions with regards to automorphism groups.

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V; A0 ; rhs/ be an arithmetic circuit over Z. 50 we can assume that C is univariate. Moreover, we can assume that C is in normal form. Hence, every right-hand side of C is either 1, 1, a variable, X C Y , or X Y for gates X and Y . C / and let r be the number of gates of C and k D r C 1. x/ is at most 2r D 2k =2. b/j Ä a2 . a/ D 0 for a randomly chosen element a 2 A is at most 1=2. a/ ¤ 0. a/ can be very r large. a/j Ä 2k2 for all a 2 A, but the r binary representation of 2k2 has exponentially many bits.

3 Preliminaries from Complexity Theory 19 The class RP \ coRP is also called ZPP (zero-error probabilistic polynomial time). Note that P Â ZPP. 45 (BPP). A language L belongs to the class BPP (bounded error probabilistic polynomial time) if there exists a nondeterministic polynomial time bounded Turing machine M and a constant such that for every input x we have: • if x 2 6 L, then ProbŒM accepts x Ä 1=2 . • if x 2 L, then ProbŒM accepts x 1=2 C . The constant (the probability gap) can be made larger by probability amplification.

U; v/ with uv 1 2 R [ R 1 and u ¤ " allow to cut off cells from a van Kampen diagram that have a nontrivial intersection with the boundary, where u is the part of the cell that belongs to the boundary. aa 1 ; "/ allow to remove boundary edges e, where one endpoint is only adjacent with edge e. , [147]. n/ C n steps, where m the maximal length of a relator in R (which is a constant in our consideration). A nondeterministic Turing machine simply guesses such a sequence of rewrite steps. u; v/ 2 T , then (i) either v D " and the next rewritten factor covers the last symbol of x or the first symbol of y or (ii) v ¤ " and the next rewritten factor covers a position in v.